Alparslan Celik and six others were remanded in custody yesterday by the court in the Aegean city of Izmir, the Dogan news agency reported. A date for the trial has yet to be set.
Celik was arrested while eating at a restaurant with friends in Izmir last week. Police seized a Kalashnikov, radios, six pistols and bullets after acting on a tip-off.
Celik has been accused by Russia of killing Russian pilot Oleg Peshkov in cold blood as he parachuted to the ground after his plane was shot down by Turkish air forces on the Syrian border on November 24.
His detention in Turkey, on charges of possessing illegal firearms, is not directly linked to the incident with the Russian pilot but Celik's lawyer swiftly denounced the move as political.
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"What is on trial is not my client but patriotism. There are major political factors at play here," said lawyer Naci Tatac.
Celik, the son of a prominent local politician from the Nationalist Movement Party (MHP), had since 2014 been fighting alongside Turkmen forces in Syria.
The Turkmen, one of majority Arab Syria's ethnic minorities, speak a language very similar to modern Turkish and are staunch allies of Ankara in fighting forces of Russia's ally Syrian President Bashar al-Assad.
Russia's ambassador to Ankara Andrei Karlov in December directly accused Celik of shooting Peshkov.
Ankara has on occasion shown signs of wanting to calm the row with Moscow, which has made the arrest of Celik one of its conditions for normalising relations.